1. Field of the Invention
The present invention relates to an optical information processing method and an apparatus therefor, and more particularly to such method and apparatus for controlling the wave form equalization characteristic, in information recording on or information readout from a recording medium by converging a light beam onto said recording medium.
2. Description of the Prior Art
In the present invention, the term "wave form equalization characteristic" means a characteristic for maintaining the signals obtained from an optical information processing apparatus exactly equivalent to the signals entered into said apparatus such that, in the aspect of waveform, any change such as an attenuation of amplitude at higher frequencies is prevented.
In the optical information processing apparatus such as a photo-disk memory, the automatic focusing optical system has conventionally been controlled by the control information obtained from the light beam reflected by the recording medium or disk. Such control system, generally including electromechanical components such as a magnetic actuator, inevitably results in a lack or a delay of response at high frequency components of the focus-error signals. In this manner the focusing control has a certain limit, so that the light beam may eventually become out of focus. As the result, relative to the signal recorded on the disk and having a waveform such as shown in FIG. 1A, the regenerated output wave form shows an amplitude loss in the high frequency region as shown in FIG. 1B. Also upon signal recording, the signal recording efficiency at high frequency region becomes lower due to the out-of-focus phenomenon explained above. Similar phenomena are also observable in digital signals. In this manner the conventional optical information processing method and apparatus have been associated with a deterioration in the wave form equalization characteristic due to the out-of-focus phenomenon, both in the signal recording and in the signal readout.